End mills are rotary tools that are used for machining many types of materials, from metals to plastics. They are supported by a shank which is generally cylindrical and adapted to be removably gripped by a motor driven chuck or functionally similar device. The shank graduates into a cutting portion on a single end end mill or into two cutting portions on a double end end mill. The cutting portion extends to an end of the end mill. The cutting portion has a plurality of cutting blades which are separated by flutes for carrying away the chips which are generated by the cutting operation. The cutting blades and the flutes may be parallel to the end mill's longitudinal axis, but more often arc helical. The cutting portion typically terminates with radial cutting features designed to complement the cutting action provided by the axial portions of the cutting blades.
Until now, nearly all end mills have been made from impact resistant materials such as high speed steels and ceramic-metal composites, e.g., cemented tungsten carbide. To the extent that ceramics have been used, due to their brittleness, they usually have been restricted to being employed as cutting edge inserts that are removably fixed to a body made of a more impact resistant material, e.g., a high speed steel. Rarely is a machining tool, such as an end mill, that may be subjected to side loading made monolithically from a ceramic material.
Nonetheless, ceramic materials are attractive in cutting operations because they can withstand the high temperatures generated in the cutting zone during the cutting operation much better than metals and even cemented tungsten carbides. High cutting temperatures are beneficial because they can cause the material that is being cut to flow more easily thus increasing metal removal rates and lowering the amount of force required to cut the material. What is needed is a monolithic end mill having a design that can take advantage of the benefits of ceramics while minimizing the problems caused by their inherent brittleness.